fix: remove memory leaks `kruskal.c`

[vil02]

Description of Change

There are two memory leaks in kruskal.c. This PR removes them.

References

Checklist

• [x] Added description of change
• [x] Relevant documentation/comments is changed or added
• [x] PR title follows semantic commit guidelines
• [x] Search previous suggestions before making a new one, as yours may be a duplicate.
• [x] I acknowledge that all my contributions will be made under the project's license.

Notes:

Fixes memory leaks in kruskal.c.

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